An adjustable reflector of a head-up display includes a base, a supporting frame, a control module, a pivot member, an adjusting frame and a reflecting element. A first end of the supporting frame is fixed to the base. The control module includes a flexible transmission member and a driving unit for driving the flexible transmission member to move. The pivot member is configured to move with the flexible transmission member. A first end of the adjusting frame is pivoted to the pivot member, and a second end of the adjusting frame is rotatable around the first end of the adjusting frame. A first side of the adjusting frame is slidably connected to a second end of the supporting frame. The reflecting element is arranged on a second side of the adjusting frame for reflecting a light beam generated by an image source to an optical combiner.